A microRNA (miRNA) is known as a nucleic acid molecule that inhibits expression of a gene. It is reported that a miRNA inhibits the translation of a protein encoded by a gene as a result of undergoing the following production process, for example. That is, first, a miRNA transcript (Pri-miRNA) is produced in a nucleus. The Pri-miRNA includes a cap structure at the 5′ end and poly(A) at the 3′ end. This Pri-miRNA is cleaved by a RNase (Drosha) to produce a miRNA precursor (Pre-miRNA). The Pre-miRNA has a hairpin structure including a loop region and a stem region. This Pre-miRNA is degraded by a cytoplasmic RNase (Dicer) after it is moved outside the nucleus, and is cleaved into a double-stranded miRNA (mature miRNA). The mature miRNA includes 1- to 4-mer overhang at the 3′ end of each chain. One of the strands of the double-stranded miRNA is called a guide strand and the other of the strands of the double-stranded miRNA is called a passenger strand, and the guide strand binds to a complex similar to a RNA induced Silencing Complex (RISC). Binding of this miRNA/RISC complex to the 3′ non-translation region (3′ UTR) of a specific mRNA allows the translation of a protein from the mRNA to be inhibited.
It becomes clear that miRNAs are deeply involved in biological phenomena such as differentiation, cell proliferation, and apotosis; as well as many diseases such as virus infectious diseases and cancers (Patent Document 1, Non-Patent Document 1, and Non-Patent Document 2). Thus, expectations of the application of miRNA especially to the medical field are growing.
Patent Document 1: WO 2010/056737 A2
Non-Patent Document 1: Deiters, 2009, The AAPS Journal, 12, 51-60
Non-Patent Document 1: Takeshita et al., 2010, Mol. Ther., 18, 181-187